# event-hash-missing

An anchor names an event **without its hash**.

- **Routes:** `create-backup` and `audit-history`
- **Description:** `event hash is missing: expected the hash of the event, as the previous audit or backup answered it`
- **Details:** None; `details` is an empty object.

## Why It Happens

An **anchor** names the event that a previous run ended at, by its `id` and its `hash`: **`lastBackedUpEvent`** for an incremental **[backup](/docs/eventsourcingdb/backup-and-restore)**, and **`lastAuditedEvent`** for an **[audit](/docs/eventsourcingdb/auditing-the-event-store)**. This one has an `id`, but **no `hash`**, or an empty one.

The `id` is checked first: an anchor without one, or with one that is not valid, is reported as **[`event-id-missing`](/docs/eventsourcingdb/errors/event-id-missing)** or **[`event-id-malformed`](/docs/eventsourcingdb/errors/event-id-malformed)**, and a hash that is there but not valid as **[`event-hash-malformed`](/docs/eventsourcingdb/errors/event-hash-malformed)**.

## How to Fix It

Send the anchor **as the previous backup or audit answered it**, with both its `id` and its `hash`. Sending the same request again fails the same way.

## Example

For a backup whose `lastBackedUpEvent` is `{ "id": "41" }`, EventSourcingDB answers with this error, as a line of the stream, and then ends the stream with its `end` item:

```json
{
  "type": "error",
  "data": {
    "code": "https://docs.eventsourcingdb.io/errors/event-hash-missing",
    "description": "event hash is missing: expected the hash of the event, as the previous audit or backup answered it",
    "details": {}
  }
}
```